CCR6+ MCAM+ Th17 Cell Numbers Increase in Patients with Psoriasis and Correlate with Disease Severity

Psoriasis is a chronic immune-mediated disease in which the interleukin (IL)-23/IL-17 axis plays a key role in the inflammatory cascade. We recently reported that co-expression of CCR6 and melanoma cell adhesion molecule (MCAM) in effector memory CD4 T cells (TEM) of peripheral blood might be a useful marker for T helper (Th) 17 cells. In this study, we monitored changes in TEM expressing CCR6 and MCAM using the Psoriasis Area and Severity Index (PASI) score during anti-tumor necrosis factor (TNF) therapy. We also studied CCR6+ MCAM+ Th17 cells histologically in skin biopsy samples from psoriasis patients. In psoriasis patients treated with anti-TNF therapy, the PASI score and the percentage of CCR6+ MCAM+ TEM cells in the blood changed almost in parallel. In immunohistochemical analyses, the proportions of IL-17+ T cells and MCAM+ T cells in the lesional skin of severely psoriatic patients were significantly higher than in mildly psoriatic patients (P<0.05), and the number of IL17+ T cells correlated with the PASI score (r=0.400, P<0.05). Taken together, these results indicate that CCR6+ MCAM+ Th17 cells in peripheral blood and lesional skin might play an important role in the pathology of psoriasis